In known so-called steer-by-wire (SBW) systems that include mechanical separation between the steering wheel and the steering mechanism of the front wheels such as, for example, that shown in Japanese Kokai Patent Application No. 2002-225733, a clutch is provided as a backup device for mechanically connecting the steering wheel and the steering mechanism. If a malfunction takes place in a portion of the SBW system, the clutch is quickly connected to stop the SBW control, and switching occurs to an assist control that can reduce the burden of steering on the driver.